1. Field of the Invention
The present invention concerns solid state photosensitive devices. It concerns more especially the reading stage of these devices.
2. Description of the Prior Art
The solid state photosensitive devices currently used both in the visible and the infra-red ranges are principally constituted by photonic detection and charges integration cells and by a reading device constituted by at least one charge transfer shift register receiving in parallel through the intermediary of a transfer gate the charges integrated in the integration zone of the cells and delivering them in series towards a reading stage giving at its output an image analysis electric signal.
The utilization of a charge transfer or coupled device or CCD in the reading device presents a certain number of drawbacks. Indeed, in order to obtain a correct flow of the charges from one stage to the other of the charge transfer device, it is necessary that the electric potentials increases from the CCD input towards the output. Now the, output voltage of the CCD often being limited by the maximal voltage that can be supported by the output stage, this means that the input voltage of the CCD is low, which consequently limits the quantity of charges able to be injected in the input stage. This progressive increase of the potentials can be avoided by pulsating certain voltages, but this therefore involves a greater complexity of the control electronics.
Furthermore, when the number of photonic detection cells is high, performances are limited by the inefficiency of the transfer and the transfer noise of the charge transfer device, particularly when working with large quantities of charges and at high operating frequencies.
The object of the present invention is to overcome the above-mentioned drawbacks.